Recently, a titanium oxide resp. titanium oxide hydrate coated mica pigment as used as a colorant for resins has been found to have a problem of causing discoloration (especially, yellowing) of resins with the lapse of time so that the resulting resins lose their original color. This is due to the addition of additives of a hindered amine light stabilizer (HALS), a phenolic antioxidant such as BHT, a flame retarder and an ultraviolet stabilizer to resins, to the titanium oxide-coated mica. In this connection, it is known that where titanium dioxide resp. oxide hydrate is in a resin, the titanium dioxide is catalytically activated due to light or heat energy as imparted thereto to thereby promote the interaction of the additives, or that the titanium dioxide directly reacts with the additives to cause discoloration of so-called yellowing phenomenon. (S. Okazaki, Colorants, 6, 333-341 (1987); M. Seino, Titanium Oxides (published by Gihodo Publishing Co. ), pp. 103-106; I. Jagnandan, H. Daun, T. J. Ambrosis & S. G. Gilbert, Journal of Pharmaceutical Science, 68 (7) 916 (1979); N. S. Allen, D. J. Bullen and J. F. Keller, Journal of Materials Science, 12, 1320 (1977)).
Due to the phenomenon, containers, decorative boards and other articles to be manufactured from the resins containing the materials would discolor with the lapse of time, after stored, to eventually lose their original colors.
As a method of inhibiting the catalytic activity of titanium dioxide in order to evade the phenomenon, in general, there has been provided a technique of stabilizing titanium dioxide by doping one or more of chromium compounds, silicon compounds, aluminum compounds, zinc compounds, phosphoric acid compounds and zirconium compounds thereinto or by coating one or more of them thereover.
However, if such a surface-coating method is applied to a pearly luster pigment, in general, it would result in loss of the intrinsic luster of the pearly pigment since the amount of the coat is relatively large, i.e. from 5 to 20% by weight to the weight of the pigment as coated therewith. Japanese Patent Application Laid-Open No. 1-225669 has disclosed an organic acid-coated anti-yellowing titanium dioxide pigment. In the disclosed case, since the surface-treating agent is an organic material, the coated pigment may still have its pearly luster. However, with the lapse of time, the storage stability of the coated pigment becomes unsatisfactory.